1. Field of the Invention
The present invention relates generally to macromolecule compositions and methods for their preparation and use. In particular, the present invention relates to a method for preparing macromolecule compositions by spray drying under controlled conditions which preserve protein purity and results in good powder dispersibility and other desirable characteristics.
Over the years, certain drugs have been sold in compositions suitable for forming a drug dispersion for oral inhalation (pulmonary delivery) to treat various conditions in humans. Such pulmonary drug delivery compositions are designed to be delivered by inhalation by the patient of a drug dispersion so that the active drug within the dispersion can reach the lung. It has been found that certain drugs delivered to the lung are readily absorbed through the alveolar region directly into blood circulation. Pulmonary delivery is particularly promising for the delivery of macromolecules (proteins, polypeptides, high molecular weight polysaccharides, and nucleic acids) which are difficult to deliver by other routes of administration. Such pulmonary delivery can be effective both for systemic delivery and for localized delivery to treat diseases of the lungs.
Pulmonary drug delivery can itself be achieved by different approaches, including liquid nebulizers, aerosol-based metered dose inhalers (MDI's), and dry powder dispersion devices. Aerosol-based MDI's are losing favor because they rely on the use of chlorofluorocarbons (CFC's), which are being banned because of their adverse effect on the ozone layer. Dry powder dispersion devices, which do not rely on CFC aerosol technology, are promising for delivering drugs that may be readily formulated as dry powders. Many otherwise labile macromolecules may be stably stored as lyophilized or spray-dried powders by themselves or in combination with suitable powder carriers.
The ability to deliver pharmaceutical compositions as dry powders, however, is problematic in certain respects. The dosage of many pharmaceutical compositions is often critical, so it is desirable that dry powder delivery systems be able to accurately, precisely, and reliably deliver the intended amount of drug. Moreover, many pharmaceutical compositions are quite expensive. Thus, the ability to efficiently formulate, process, package, and deliver the dry powders with a minimal loss of drug is critical. While the permeability of natural macromolecules in the lung is well known, the combined inefficiencies of macromolecule production processes and macromolecule delivery has limited commercialization of dry macromolecule powders for pulmonary delivery.
A particularly promising approach for the pulmonary delivery of dry powder drugs utilizes a hand-held device with a hand pump for providing a source of pressurized gas. The pressurized gas is abruptly released through a powder dispersion device, such as a venturi nozzle, and the dispersed powder made available for patient inhalation. While advantageous in many respects, such hand-held devices are problematic in a number of other respects. The particles being delivered are usually less than 5 μm in size, making powder handling and dispersion more difficult than with larger particles. The problems are exacerbated by the relatively small volumes of pressurized gas, which are available using hand-actuated pumps. In particular, venturi dispersion devices are unsuitable for difficult-to-disperse powders when only small volumes of pressurized gas are available with the handpump. Another requirement for hand-held and other powder delivery devices is efficiency. High device efficiency in delivering the drug to the patient with the optimal size distribution for pulmonary delivery is essential for a commercially viable product. Conventional techniques used to deliver medication do not have the delivery efficiency required for commercialization. The ability to achieve both adequate dispersion and small dispersed volumes is a significant technical challenge that requires that each unit dosage of the powdered composition be readily and reliably dispersible.
Spray drying is a conventional chemical processing unit operation used to produce dry particulate solids from a variety of liquid and slurry starting materials. The use of spray drying for the formulation of dry powder pharmaceuticals is known, but has usually been limited to small molecule and other stable drugs which are less sensitive to thermal degradation and other rigorous treatment conditions. The use of spray drying for the preparation of biological macromolecule compositions, including proteins, polypeptides, high molecular weight polysaccharides, and nucleic acids, can be problematic since such macromolecules are often labile and subject to degradation when exposed to high temperatures and other aspects of the spray drying process. Excessive degradation of the macromolecules can lead to drug formulations lacking in the requisite purity. It can also be difficult to control particle size and particle size distribution in compositions produced by spray drying. For pulmonary delivery, it is critical that the average particle size be maintained below 5 μm, preferably in the range from 0.4 μm to 5 μm, and that the amount of the composition comprising particles outside of the target size range be minimized. Preferably, at least 90% by weight of the powder will have a particle size in the range from 0.1 μm to 7 μm. More preferably, at least 95% will have a size in the range from 0.4 μm to 5 μm. Moreover, it can sometimes be difficult to achieve a desired low moisture content required for physical and chemical stability in the final particulate product, particularly in an economic manner. Finally, and perhaps most important, it has been difficult to produce the small particles necessary for pulmonary delivery in an efficient manner. For high value macromolecular drugs, collection efficiencies (i.e., the amount of particulate drug recovered from the process in a useable form) should be above 80% by weight, preferably above 90% by weight, and desirably above 95% by weight. While spray drying has been used to prepare powder of macromolecules in laboratory scale equipment as described below, commercial spray driers are not designed to produce powders in the pulmonary size range. The methods for atomization, drying powder, and collection must be modified to economically produce a protein powder with the desired product characteristics for pulmonary delivery and in sufficient yield and at commercially acceptable production rates (in excess of 30 g/hr).
It is therefore desirable to provide improved methods for the spray drying of macromolecules for use in pulmonary and other drug delivery. In particular, it is desirable to provide improved process methods and powder composition which address at least some of the deficiencies listed above.
2. Description of the Background Art
U.S. Pat. Nos. 5,260,306, 4,590,206, GB 2 105 189, and EP 072 046 describe a method for spray drying nedocromil sodium to form small particles preferably in the range from 2 to 15 μm for pulmonary delivery. U.S. Pat. No. 5,376,386, describes the preparation of particulate polysaccharide carriers for pulmonary drug delivery, where the carriers comprise particles sized from 5 to 1000 μm and having a rugosity less than 1.75. Mumenthaler et al., (1994) Pharm. Res. 11:12 describes recombinant human growth hormone and recombinant tissue-type plasminogen activator. That study demonstrated that the proteins may degrade during spray drying and hence may not retain sufficient activity for therapeutic use. WO 95/23613 describes preparing an inhalation powder of DNase by spray drying using laboratory-scale equipment. WO 91/16882 describes a method for spray drying proteins and other drugs in liposome carriers.
The following applications assigned to the assignee of the present application each describe that spray drying may be used to prepare dry powders of biological macromolecules: application Ser. No. 08/423,515, filed on Apr. 14, 1995; application Ser. No. 08/383,475, which was a continuation-in-part of application Ser. No. 08/207,472, filed on Mar. 7, 1994; application Ser. No. 08/472,563, filed on Apr. 14, 1995, which was a continuation-in-part of application Ser. No. 08/417,507, filed on Apr. 4, 1995, now abandoned, which was a continuation of application Ser. No. 08/044,358, filed on Apr. 7, 1993, now abandoned; application Ser. No. 08/232,849, filed on Apr. 25, 1994, which was a continuation of application Ser. No. 07/953,397, now abandoned. WO 94/07514 claims priority from Ser. No. 07/953,397. WO 95/24183 claims priority from Ser. Nos. 08/207,472 and 08/383,475.